Recognize images with uppercase extensions

Fixes: #6472

src/Text/Pandoc/Readers/Org/Shared.hs

@@ -26,7 +26,8 @@ import Text.Pandoc.Shared (elemText)
 isImageFilename :: Text -> Bool
 isImageFilename fp = hasImageExtension && (isValid (T.unpack fp) || isKnownProtocolUri)
  where
-   hasImageExtension = takeExtension (T.unpack fp) `elem` imageExtensions
+   hasImageExtension = takeExtension (T.unpack $ T.toLower fp)
+                       `elem` imageExtensions
    isKnownProtocolUri = any (\x -> (x <> "://") `T.isPrefixOf` fp) protocols
 
    imageExtensions = [ ".jpeg", ".jpg", ".png", ".gif", ".svg" ]

test/Tests/Readers/Org/Inline.hs

@@ -214,6 +214,10 @@ tests =
                 , "[[file:guinea-pig.gif]]"
                 ] =?>
       para (imageWith ("", [], [("width", "50%")]) "guinea-pig.gif" "" "")
+
+    , "Uppercase extension" =:
+      "[[file:test.PNG]]" =?>
+      para (image "test.PNG" "" "")
     ]
 
   , "Explicit link" =: